It depends on if you are talking about shop or field work. I agree with david's post above for shop work, however if you install a galvanized handrail in the field SMAW would be better.
Be sure to protect your welders from zinc fumes either way. A proper respirator should be worn during welding. Zinc sickness/poisoning is pretty nasty.
Where possible grind the zinc off the areas to be welded, touch up with Zinc rich spray paint after.
Ideally Fabricate from bare steel, Hot dip Galvanize after, mask off areas to be field welded.
B.E.
You are judged not by what you know, but by what you can do.
I chose GMAW for speed. In a shop, it is much more efficient. In the field, as others have stated, there are additional things to consider..and SMAW is usually the simplest to implement (wind is not such a big factor with SMAW, and lead length is usually much longer).
You can also use flux core in the field , it is less sensitive to wind and the operator can set up a fan behind them to assist in keeping the fumes out of the welding helmet. I have attached an article that may help.
B.E.
You are judged not by what you know, but by what you can do.
